1. Field of the Invention
The present invention relates to an image conversion method and an image conversion apparatus for allowing a matrix type fix display device, such as a liquid crystal display, to display image signals of various types of systems.
2. Description of the Background Art
Among methods which are used to display image signals of various types of systems in a matrix type fix display device are, as introduced in xe2x80x9cImage Analysis Handbook (University of Tokyo Press),xe2x80x9d nearest neighbor interpolation, bi-linear interpolation, cubic convolution interpolation and the like. Means for embodying such methods may be a method externally using a memory which can be accessed at random as described in U.S. Pat. No. 4,631,450, for example.
FIG. 6 is a block diagram of a conventional image conversion apparatus. In FIG. 6, frame memories 401, 403 are accessible at random and have a function of converting horizontal scanning and vertical scanning of one frame of sampled image signals and outputting the signals. A vertical conversion filter 402 executes processing for expanding or reducing an image in the vertical direction. A horizontal conversion filter 404 executes processing for expanding or reducing an image in the horizontal direction. An address generator 405 generates horizontal addresses and vertical addresses which are to be supplied to the frame memory 401 as well as to the vertical conversion filter 402. An address generator 406 generates horizontal addresses and vertical addresses which are to be supplied to the frame memory 403 as well as to the horizontal conversion filter 404.
Next, operations of the image conversion apparatus will be described. In the image conversion apparatus, first, input image signals are written in the frame memory 401 in the order of horizontal scanning of the input signals, in accordance with outputs from the address generator 405, namely, write addresses. The frame memory 401 reads in the order of vertical scanning, in accordance with outputs from the address generator 405, namely, read addresses, for the purpose of conversion of horizontal scanning into vertical scanning.
The signals thus read out are supplied to the vertical conversion filter 402 which thereafter expands or reduces the signals in the vertical direction. At this stage, as the address generator 405 supplies addresses to the vertical conversion filter 402, depending on the contents of these addresses, read addresses in the frame memory 401 may be changed to thereby accordingly control (change) a filtering characteristic of the vertical conversion filter 402. That is, as the addresses are supplied, it is possible to change the filtering characteristic (filtering contents) in accordance with vertical positions.
Next, outputs from the vertical conversion filter 402 are written in the frame memory 403 in the order of the outputs in accordance with outputs from the address generator 406, namely, write addresses. For conversion of vertical scanning into horizontal scanning, the frame memory 403 reads in the order of horizontal scanning in accordance with outputs from the address generator 406, namely, read addresses.
Image signals outputted from the frame memory 403 are in the horizontal and vertical scanning condition of the input image signals which were supplied to the frame memory 401.
The signals read from the frame memory 403 are thereafter supplied to the horizontal conversion filter 404 which then expands or reduces the images in the horizontal direction. At this stage, as the address generator 406 supplies addresses to the horizontal conversion filter 404, depending on the contents of these addresses, read addresses in the frame memory 403 may be changed to thereby accordingly control (change) a filtering characteristic of the horizontal conversion filter 404. That is, as the addresses are supplied, it is possible to change the filtering characteristic (filtering contents) in accordance with horizontal positions.
However, in a structure according to the conventional technique as described above, where one wishes to use filtering means of a multi-tap structure for handling a large quantity of pixel data which are needed for processing, it is necessary to execute a memory access for reading the pixel data from a frame memory at a speed which is defined as a cycle speed of the pixel data multiplied by the number of the taps of the filtering means.
As herein termed, filtering refers to interpolation in pixel conversion processing. However, in a broad sense, filtering also means bandwidth restriction processing, aperture processing, etc.
For example, where input image signals is XGA signals (1,024 dots in the horizontal directionxc3x97768 dots in the vertical direction) of 60 Hz and 4-tap filtering means is to be used, since a cycle speed of pixel data is 65 MHz, it is necessary to read out pixel data while accessing a frame memory at 260 MHz.
Accessing a memory at such a high speed is very difficult considering the specifications of currently available memories, and hence, can not be realized without a difficulty.
The present invention aims at providing an image conversion method, an image conversion apparatus and a liquid crystal projector for realizing image conversion utilizing filtering processing with a multi-tap structure without requiring a memory to use a high-speed capability.
A first aspect of the present invention is directed to an image conversion method in which output image signals are generated through filtering processing which uses a plurality pieces of continuous pixel data of input image signals which are sampled, wherein pixel data of approximately one frame of said input image signals are stored in first memory means, a larger quantity of continuous pixel data containing a plurality pieces of continuous pixel data needed for said filtering processing are read in advance from said first memory means and stored in second memory means, the plurality pieces of continuous pixel data needed for said filtering processing are selected from said second memory means, and said output image signals are generated through said filtering processing which uses the selected plurality pieces of pixel data.
According to the method described above, it is possible to output a plurality pieces of continuous pixel data from the first memory means for one access and select necessary pixel data from the second memory means, and therefore, it is possible to realize image conversion which does not require high-speed memory accessing.
A third aspect of the present invention is directed to an image conversion apparatus which generates output image signals through filtering processing which uses a plurality pieces of continuous pixel data of input image signals which are sampled, comprising: filtering means which generates said output image signals from said plurality pieces of continuous pixel data; merging means which receives said input image signals, and merges and outputs said input image signals for every plurality pieces of continuous pixel data; first memory means which receives an output from said merging means and stores pixel data of approximately one frame; second memory means which receives an output from said first memory means, and stores and outputs a larger quantity of continuous pixel data than a plurality pieces of continuous pixel data required by said filtering means; selecting means which receives an output from said second memory means, and selects and outputs the plurality pieces of continuous pixel data required by said filtering means; and third memory means which stores and outputs address data which are calculated in advance to control an output from said first memory means and control data which are calculated in advance to control a filter factor of said filtering means, wherein said filtering means receives an output from said selecting means, and in accordance with the address data in said third memory means, said first memory outputs a larger quantity of pixel data than the pixel data which are required by said filtering means.
The structure above allows to output a plurality pieces of continuous pixel data from the first memory means for one access and select necessary pixel data from the second memory means and the selecting means, and therefore, it is possible to realize image conversion utilizing filtering with a multi-tap structure which does not require high-speed memory accessing and ensure that image conversion processing produces a high image quality. Further, as the third memory means stores data which are calculated in advance based on desired magnifications for reduction conversion and expansion magnification, it is possible to convert at various magnifications.
An eighth aspect of the present invention is directed to an image conversion apparatus which generates output image signals through filtering processing which uses a plurality pieces of continuous pixel data of input image signals which are sampled, comprising: filtering means which generates output image signals from said plurality pieces of continuous pixel data; merging means which receives said input image signals, and merges and outputs said input image signals for every plurality pieces of continuous pixel data; first, second and third memory means which receive an output from said merging means and store pixel data of approximately one frame; first selecting means which receives outputs from said first, said second and said third memory means, and selects and outputs any one of the outputs from said first, said second and said third memory means; fourth memory means which receives an output from said first selecting means, and stores and outputs a larger quantity of continuous pixel data than a plurality pieces of continuous pixel data required by said filtering means; second selecting means which receives an output from said fourth memory means, and selects and outputs the plurality pieces of continuous pixel data required by said filtering means; and fifth memory means which stores and outputs address data which are calculated in advance to control the outputs from said first, said second and said third memory means and control data which are calculated in advance to control a filter factor of said filtering means, wherein said first, said second and said third memory means repeatedly write pixel data of different sequential frames of said input signals, said first selecting means selects any one of said first, said second and said third memory means which completed writing, said filtering means receives the output from said second selecting means, and in accordance with the address data in said fifth memory means, said first, said second and said third memory means output a larger quantity of pixel data than the pixel data which are required by said filtering means.
The structure above allows to output a plurality pieces of continues pixel data from the first, the second and the third memory means for one access. Further, the first, the second and the third memory means store pixel data of continuos three frames of continuous input image signals. A speed for writing pixel data to the first, the second and the third memory means and a speed for reading pixel data from the first, the second and the third memory means can be different from each other. The fourth memory means and the second selecting means can select necessary pixel data. Hence, it is possible to realize conversion of a frame frequency and image conversion utilizing filtering with a multi-tap structure which does not require high-speed memory accessing and ensure that image conversion produces a high image quality. In addition, use of the first, the second and the third memory means allows that the memory means for storing outputs from the merging means is different from the memory means for outputting to the first selecting means, it is possible to eliminate conflict between storing and outputting within the same memory means, and hence, to simplify control of the memory means. Further, as the fifth memory means store data which are calculated in advance based on desired magnifications for reduction conversion and expansion magnification, it is possible to convert at various magnifications.
A thirteenth aspect of the present invention is directed to a liquid crystal projector which generates output image signals through filtering processing which uses a plurality pieces of continues pixel data of input image signals which are sampled, comprising: filtering means which generates output image signals from said plurality pieces of continuos pixel data; merging means which receives said input image signals, and merges and outputs said input image signals for every plurality pieces of continues pixel data; first, second and third memory means which receive an output from said merging means and store pixel data of approximately one frame; first selecting means which receives outputs from said first, said second and said third memory means, and selects and outputs any one of the outputs from said first, said second and said third memory means; fourth memory means which receives an output from said first selecting means, and stores and outputs a larger quantity of continuous pixel data than a plurality pieces of continuous pixel data required by said filtering means; second selecting means which receives an output from said fourth memory means, and selects and outputs the plurality pieces of continuous pixel data required by said filtering means; fifth memory means which stores and outputs address data which are calculated in advance to control the outputs from said first, said second and said third memory means and control data which are calculated in advance to control a filter factor of said filtering means; driving means which receives an output from said filtering means and executes processing for displaying; a liquid crystal panel which receives an output from said driving means and modulates light in accordance with an input to said liquid crystal panel; a lamp; lighting means which turns on said lamp; converging means which converges light emitted from said lamp and irradiates the light upon said liquid crystal panel; and projecting means which projects light passing through said liquid crystal panel of illumination from said projecting means, wherein said first, said second and said third memory means repeatedly write pixel data of different sequential frames of said input signals, said first selecting means selects any one of said first, said second and said third memory means which completed writing, said filtering means receives the output from said second selecting means, and in accordance with the address data in said fifth memory means, said first, said second and said third memory means output a larger quantity of pixel data than the pixel data which are required by said filtering means.
The structure above allows to output a plurality pieces of continues pixel data from the first, the second and the third memory means for one access. Further, the first, the second and the third memory means store pixel data of continuos three frames of continuous input image signals. A speed for writing pixel data to the first, the second and the third memory means and a speed for reading pixel data from the first, the second and the third memory means can be different from each other. The fourth memory means and the second selecting means can select necessary pixel data. Hence, it is possible to realize a liquid crystal projector having a high image quality which performs conversion of a frame frequency and image conversion utilizing filtering with a multi-tap structure which does not require high-speed memory accessing. In addition, use of the first, the second and the third memory means allows that the memory means for storing outputs from the merging means is different from the memory means for outputting to the first selecting means, it is possible to eliminate conflict between storing and outputting within the same memory means, and hence, to simplify control of the memory means. Further, as the fifth memory means store data which are calculated in advance based on desired magnifications for reduction conversion and expansion magnification, it is possible to convert at various magnifications.